Ethylene-propylene-diene dicyclopentadiene

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

As was mentioned, cycloaddition of unactivated hydrocarbons, namely, that of cyclopentadiene, has practical significance. 5-Vinyl-2-norbomene is produced by the cycloaddition of cyclopentadiene and 1,3-butadiene546,547 [Eq. (6.96)] under conditions where side reactions (polymerization, formation of tetrahydroindene) are minimal. The product is then isomerized to 5-ethylidene-2-norbomene, which is a widely used comonomer in the manufacture of an EPDM (ethylene-propylene-diene monomer) copolymer (see Section 13.2.6). The reaction of cyclopentadiene (or dicyclopentadiene, its precursor) with ethylene leads to norbomene548,549 [Eq. (6.97)] 550... 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

When ethylene is copolymerized with substantial amounts (>25%) of propylene an elastomeric copolymer is produced, commonly known as ethylene-propylene rubber (EPR) or ethylene-propylene monomer (EPM) rubber. When a diene, such as dicyclopentadiene, is also included, a terpolymer known as ethylene-propylene-diene monomer (EPDM) rubber is obtained. EPR and EPDM are produced with single site and Ziegler-Natta catalysts and are important in the automotive and construction industries. However, EPR and EPDM are produced in much smaller quantities relative to polyethylene. Elastomers display vastly different properties than other versions of industrial polyethylene and are considered outside the purview of this text. EPR and EPDM will not be discussed further. 

Ethylene/propylene co-polymers (usually called EPRs for ethylene-propylene rubbers, or EPMs for ethylene-propylene monomers) are amorphous polyolefins when the propylene content is in the range 30-70%. Despite the typical unreactivity of saturated polyolefins, ethylene-rich EP co-polymers can be made highly elastic by radical cross-linking, but in order to make the rubber vulcanizable , a diene (5-ethylidene-2-norbornene, 1,4-hexadiene, or dicyclopentadiene) is added, which leaves one unreacted double bond available for subsequent cross-linking. These latter materials are called EPDMs (for ethylene-propylene-diene monomers). 

Copolymerization of ethylene and propylene produces an elastomeric polymer that is virtually inert because of the absence of carbon-carbon double bonds (EPM). Such polymers thus tend to be crossUnked with peroxides or by radiation. To improve the reactivity of ethylene-propylene copolymers, 1-10% of a third monomer can be added to give a terpolymer or ethylene-propylene-diene monomer (EPDM). The primary diene monomers used in EPDM are 1,4-hexadiene, dicyclopentadiene, and ethyUdene norbomene. Introduction of an unsaturated monomer such as ethylidene norbomene will enable use of sulfur-based crosslinking systems. 

PGC has been used to determine the overall composition of ethylene-propylene-diene terpolymers [10]. In attempting to determine the third component in these materials, difficulties might be anticipated, since this component is normally present in amounts around 5 wt%. However, dicyclopentadiene was identified in ethylene-propylene-diene terpolymers even when the amount incorporated was very low. 

Polymerization of ethylene and propylene results in a saturated copolymer. In order to vulcanize this rubber, some unsaturation has to be introduced. This is commonly done by adding a few percent of non-conjugated diene (termonomer) such as dicyclopentadiene, 1,4-hexadiene, or ethylidene norborene during the polymerization. Since only one of the double bonds of the diene reacts during polymerization, the other is free for vulcanization. The amount of unsaturation left in the ethylene propylene diene terpolymer is of great interest because the vulcanization properties will be affected. 

Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

An elastomer consisting of a terpolymer of ethylene, propylene and a diene, e.g., dicyclopentadiene. 

Another of the monomers used in addition to ENB is dicyclopentadiene (DCPD), which is shown in Figure 8.9. As can be seen from the structure, there are two double bonds in DCPD. Each of the two dienes will have different tendencies for long chain branching, which will influence processing rates and cross-linking by sulfur or peroxide cures [3], Table 8.5 shows some of the characteristics of the two dienes [5], In addition, Table 8.6 shows general features of ethylene-propylene elastomers as related to the ter-... 

Copolymerization of ethylene with propylene results in a random, noncrystalline copolymer that is a chemically inert and rubbery material. EPM is a saturated copolymer that can be cross-linked through the combination of the free radicals generated by peroxides or radiation. To incorporate sites for vulcanization, an unsaturated terpolymer can be prepared from ethylene, propylene, and a small amount (3 to 9%) of a nonconjugated diene (EPDM). The diene is either dicyclopentadiene, ethylidene nor-bomene, or 1,4-hexadiene. The resulting unsaturated terpolymer can be vulcanized by traditional techniques. Each of the termonomers confers different characteristics on the final elastomer. 

From other p<%olefins, photocrossiinking of ethylene propylene da omers, copolymerized with dienes such as dicyclopentadiene, 1.4-hexadiene, and 5-ethylidene... 

Triple ethylene-propylene rubbers of SKEP(T) brands contain up to several percents of non-conjugated dienes predominantly dicyclopentadiene (DCPD) and ethylidennorbomene (ENB) as third comonomers [177]. 

Altenau and co-workers [111] applied time-averaging NMR to the determination of low percentages of termonomers such as 1,4-hexadiene, dicyclopentadiene and ethylidene norbornene in ethylene-propylene termonomers. They compared results obtained by NMR and the iodine monochloride procedure of Lee and co-workers [81]. The chemical shifts and splitting pattern of the olefinic response were used to identify the termonomer. Figure 3.11 shows the time-averaged NMR spectra of ethylene-propylene terpolymers containing various dienes. 

The diene ethylidiene norbornene in Vistalon EPDM allows sulfur vulcanization (see Table 3.12). 1,4-Hexadiene and dicyclopentadiene (DCPD) are also used as curing agents.The completely saturated polymer backbone precludes the need for antioxidants that can bleed to the surface (bloom) of the finished product and cause staining. Saturation provides inherent ozone and weather resistance, good thermal properties, and a low compression set. Saturation also allows a relatively high-volume addition of low-cost fillers and oils in compounds while retaining a high level of mechanical properties. The ethylene/propylene monomer ratio also affects the properties. 

An EPDM rubber is produced by the terpolymerisation of ethylene and propylene with a small amount (typically of the order of 5%) of an unconjugated di-olefin. The di-olefins used, include dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene and methyl tetrahydroindene, 1,5 cyclo octadiene. A number of other dienes [74,75] have been tried. Infrared spectroscopy [35] is used to find out the ter monomer content. The characteristic peaks for the ter monomer are shown in Table 3.4. In view of the relatively low concentrations, it is probable that ter monomer base units are present largely as isolated units in EPDM but the distribution of propylene and methylene sequences is of considerable interest. 

While the third monomer can be a conunon diene, like isoprene, more often it is a bridged ring structure with at least one double bond in the ring. In typical terpolymer rubbers with 60 to 40 ratios of ethylene to propylene, the diene components usually comprise about 3% of the total. Some specialty rubbers, however, may contain 10% of the diene or even more. Reaction conditions are always chosen to obtain 1,2 placement of the diene. Dienes in common use are ethylidine norbomene, methylene norbomene, 1,4-hexadiene, dicyclopentadiene, and cycloocadiene ... 

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